Paper, as that term is used herein, refers to the wide variety of cellulose-based sheet materials used for writing, printing, packaging, and other applications. Paper may be used, for example, but without limitation, in the following applications: as paper money, bank notes, stock and bond certificates, checks, postage stamps, and the like; in books, magazines, newspapers, and art; for packaging, e.g., paper board, corrugated cardboard, paper bags, envelopes, wrapping tissue, boxes; in household products such as toilet paper, tissues, paper towels and paper napkins; paper honeycomb, used as a core material in composite materials; building materials; construction paper; disposable clothing; and in various industrial uses including emery paper, sandpaper, blotting paper, litmus paper, universal indicator paper, paper chromatography, battery separators, and capacitor dielectrics.
In some applications, for example when paper is used as currency and in other financial applications, it is often desirable to be able to “mark” or “tag” the paper with a special marking that is not visible to the naked eye, and/or cannot easily be produced by counterfeiters. Marking can be used, for example, to prevent or detect counterfeiting of currency, art and other valuable documents. Marking can also be used on currency to allow the currency to be traced and/or identified, e.g., if it is stolen or used in a criminal transaction.